1. Field of the Invention
The present invention relates to a magnetic random access memory (MRAM) in which a memory cell is constructed using MTJ (Magnetic Tunnel Junction) elements having “1”, “0”-information stored therein by a tunneling magneto resistive effect.
2. Description of the Related Art
In recent years, there have been proposed many memories having information stored therein by new principle, and one of them is a memory using a tunneling magneto resistive (hereinafter, denoted as TMR) effect proposed by Roy Scheuerlein et. al (for example, refer to ISSCC2000 Technical Digest p. 128 “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each cell”).
The magnetic random access memory stores “1”, “0”-information by the MTJ elements. The MTJ elements have a structure in which an insulation layer (tunnel barrier) is sandwiched with two ferromagnetic layers. The information stored in the MTJ elements is determined by whether or not the orientations of spins of the two ferromagnetic layers are parallel or anti-parallel.
Here, parallel means that the orientations of the spins of the two ferromagnetic layers are same, and anti-parallel means that the orientations of the spins of the two ferromagnetic layers are opposite to each other.
Generally, one of the two ferromagnetic layers constructing the MTJ element is a pin layer in which the orientation of the spin is pinned. When “1”, “0”-information is stored in the MTJ elements, the orientation of the other one (free layer) of the two ferromagnetic layers is varied according to written information.